The present invention relates to chiral compounds and to their use as chiral dopants for nematic or cholesteric liquid crystals for the generation of layers which reflect in color in the UV or IR region or for the preparation of pigments having a liquid-crystalline, cholesteric order.
Cholesteric liquid crystals (CLCs) reflect circular-polarized electromagnetic radiation in a wavelength region which is dependent on the helical structure of the CLC. The central wavelength of the reflection band is determined by the pitch p of the helical structure, and the width of the band is determined by the optical anisotropy of the mesogens. The central wavelength of the reflection band, which is referred to below as the reflection wavelength, is dependent on the viewing angle. The direction of rotation of the reflected light corresponds to the direction of rotation of the cholesteric helix.
Cholesteric liquid-crystal mixtures generally comprise one or more optically active components for inducing a chiral structure. For example, cholesteric liquid-crystal mixtures can consist of a nematic base material and one or more optically active dopants, which generate either a right- or left-handed twist in the nematic phase which determines the direction of rotation of the reflected circular-polarized light.
Numerous compounds have been disclosed as chiral dopants for liquid-crystalline phases (for example in DE-A 43 42 280, DE-A 195 41 820 and DE-A 196 11 101, and in GB-A-2 314 839 and WO 98/00428).
For left-handed helical materials, cholesterol compounds are frequently suitable; apart from chirality, these introduce sufficiently mesogenic properties in order to generate a stable mesophase. Such compounds are described, for example, by H. Finkelmann, H. Ringsdorf et al., in Makromol. Chem. 179, 829-832 (1978). However, these compounds have the disadvantage of complex synthesis and a high preparation price.
It is an object of the present invention to provide novel chiral compounds which are suitable for the preparation of cholesteric liquid-crystalline compositions and which do not have the abovementioned disadvantages.
We have found that this object is achieved in accordance with the invention by the use of compounds of the general formula I 
in which the substituents, independently of one another, have the following meanings:
R1 is Z1xe2x80x94Y1xe2x80x94(A1)mxe2x80x94Y2xe2x80x94M1xe2x80x94Y3xe2x80x94(A2)nxe2x80x94Y4xe2x80x94;
R2 is hydrogen, C1-C12-alkyl, C1-C12-alkylcarbonyl, aryl, arylcarbonyl or Z2xe2x80x94Y5xe2x80x94(A3)oxe2x80x94Y6xe2x80x94M2xe2x80x94Y7xe2x80x94(A4)pxe2x80x94Y11xe2x80x94;
R3 is hydrogen, C1-C12-alkyl, aryl or OR5;
R4 is hydrogen, C1-C12-alkyl, aryl or OR6;
R5 and R6 are hydrogen, C1-C12-alkyl, C1-C12-alkylcarbonyl, aryl, arylcarbonyl or Z3xe2x80x94Y8xe2x80x94(A5)qxe2x80x94Y9xe2x80x94M3xe2x80x94Y10xe2x80x94(A6)rxe2x80x94Y12xe2x80x94;
A1 to A6 are spacers having a chain length of from 1 to 30 carbon atoms;
M1 to M3 are mesogenic groups;
Y1 to Y10 are chemical bonds, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94, xe2x80x94C(xe2x95x90O)xe2x80x94N(R)xe2x80x94 or xe2x80x94(R)Nxe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94CH2xe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94, xe2x80x94Nxe2x95x90CHxe2x80x94 or xe2x80x94Nxe2x95x90Nxe2x80x94;
Y11 and Y12 are chemical bonds, xe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94(R)Nxe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94CH2xe2x80x94 or xe2x80x94Oxe2x80x94CH2xe2x80x94;
R is hydrogen or C1-C4-alkyl;
Z1 to Z3 are hydrogen, C1-C12-alkyl, polymerizable groups or radicals carrying polymerizable groups;
m to r is are 0 or 1,
where the radicals A1 to A6, Y1 to Y10, Y11 and Y12 and Z1 to Z3 may be identical or different, and where, in the case where one or more of the indices m to r are zero, at least one of the radicals Y in each case adjacent to A is a chemical bond,
as chiral dopants for nematic or cholesteric liquid crystals for the generation of layers which reflect in color in the UV or IR region or for the preparation of pigments having a liquid-crystalline, cholesteric order.
Examples of alkyl radicals which may be mentioned for R2 to R6 and for Z1 to Z3 are branched or unbranched C1-C12-alkyl chains, for example methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 3,3-dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-1-methylpropyl, 1-ethyl-2-methylpropyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, n-undecyl and n-dodecyl.
Preferred alkyl radicals which may be mentioned for R2 to R6 from the abovementioned list are the branched or unbranched C1-C6-alkyl chains, for example methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, 2-ethylpropyl and n-hexyl.
Preferred alkyl radicals which may be mentioned for Z1 to Z3 from the abovementioned list are the branched or unbranched C4-C10-alkyl chains, for example n-butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, 1-ethylpropyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl and n-decyl.
The term xe2x80x9carylxe2x80x9d for R2 to R6 is taken to mean aromatic rings or ring systems having 6 to 18 carbon atoms in the ring system, for example phenyl or naphthyl, which can be unsubstituted or substituted by one or more radicals, such as halogen, for example fluorine, chlorine or bromine, cyano, nitro, amino, C1-C4-alkylamino, C1-C4-dialkylamino, hydroxyl, C1-C4-alkyl, C1-C4-alkoxy or other radicals.
Alkyl and arylcarbonyl radicals which may be mentioned for R2, R5 and R6 are carbonyl groups with the abovementioned C1-C12-alkyl chains or the abovementioned aromatic rings or ring systems having 6 to 18 carbon atoms.
Suitable spacers A1 to A6 are all groups known for this purpose. The spacers generally contain from 1 to 30, preferably from 1 to 12, particularly preferably from 1 to 6, carbon atoms and consist of predominantly linear aliphatic groups. They may be interrupted in the chain, for example by non-adjacent oxygen or sulfur atoms or imino or alkylimino groups, for example methylimino groups. Suitable substituents for the spacer chain are fluorine, chlorine, bromine, cyano, methyl and ethyl.
Examples of representative spacers are the following:
xe2x80x94(CH2)uxe2x80x94, xe2x80x94(CH2CH2O)vCH2CH2xe2x80x94, xe2x80x94CH2CH2SCH2CH2xe2x80x94, xe2x80x94CH2CH2NHCH2CH2xe2x80x94, 
xe2x80x83where u is from 1 to 12, and v is from 1 to 3.
Preferred spacers are ethylene, propylene, n-butylene, n-pentylene and n-hexylene.
It is furthermore also possible to link one or more of the mesogenic radicals M1 to M3 directly to the associated radicals Z1 to Z3 without spacers. In these cases, the indices m, o and q are 0, and Y1/Y2, Y5/Y6 and Y8/Y9 together are a chemical bond, in particular a single chemical bond.
The radicals M1 to M3 can be all known mesogenic groups.
Particularly suitable mesogenic groups are those of the formula
(xe2x80x94Txe2x80x94Y17)wxe2x80x94Txe2x80x94
in which the variables have the following meanings:
T are identical or different divalent, saturated or unsaturated, isocyclic or heterocyclic radicals,
Y17 are groups as defined for Y1 to Y10, and
w is 0, 1, 2 or 3,
where, in the case where w greater than 0, both the radicals T and the groups Y17 may in each case be identical to or different from one another.
w is preferably 1 or 2.
The radicals T may also be ring systems which are substituted by fluorine, chlorine, bromine, cyano, hydroxyl or nitro. Preferred radicals T are the following: 
Examples of preferred mesogenic groups M are the following: 
Particular preference is given to mesogenic groups M of the following formulae 
where each aromatic ring may carry up to three identical or different substituents from the following group:
hydrogen, C1-C20-alkyl, C1-C20-alkoxy, C1-C20-alkoxycarbonyl, C1-C20-monoalkylaminocarbonyl, C1-C20-alkylcarbonyl, C1-C20-alkylcarbonyloxy, C1-C20-alkylcarbonylamino, formyl, halogen, cyano, hydroxyl and nitro.
Besides hydrogen, fluorine, chlorine, bromine, cyano, formyl and hydroxyl, preferred substituents for the aromatic rings are, in particular, short-chain aliphatic radicals, such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl, tert-butyl and alkoxy, alkoxycarbonyl, alkylcarbonyl, alkylcarbonyloxy, alkylcarbonylamino and monoalkylaminocarbonyl radicals which contain these alkyl groups.
The outer benzene rings of the particularly preferred groups M preferably have the following substitution patterns: 
or they are substituted analogously by F, Br, CH3, OCH3, CHO, COCH3, OCOCH3 or CN instead of Cl, where the substituents may also be mixed. Mention may furthermore be made of the structures 
in which x is from 2 to 20, preferably from 8 to 15.
The preferred substitution patterns of the central benzene ring of the particularly preferred groups M are 
Alkyl radicals which may be mentioned for R and for branched or unbranched C1C4-alkyl chains are preferably methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl and 1,1-dimethylethyl.
Preferred radicals for Z1 to Z3 are the following: 
xe2x80x94Nxe2x95x90Cxe2x95x90O, xe2x80x94Nxe2x95x90Cxe2x95x90S, xe2x80x94Oxe2x80x94Cxe2x89xa1N, xe2x80x94COOH, xe2x80x94OH and NH2
where the radicals R8 to R10 may be identical or different and are hydrogen or C1-C4-alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl. Of the reactive polymerizable groups, the cyanates can spontaneously trimerize to cyanurates and are therefore preferred. The other groups mentioned require further compounds containing complementary reactive groups for polymerization. Thus, for example, isocyanates can polymerize with alcohols to give urethanes and with amines to give urea derivatives. An analogous situation applies to thiiranes and aziridines. Carboxyl groups can be condensed to give polyesters and polyamides. The maleimido group is particularly suitable for free-radical copolymerization with olefinic compounds, such as styrene. The complementary reactive groups here can either be present in a second compound according to the invention which is mixed with the first or they can be incorporated into the polymeric network by means of auxiliary compounds containing 2 or more of these complementary groups.
Polymerizable groups which may be mentioned in particular are acrylate and methacrylate.
Particular preference is given to the chiral dopants of the general formula Ia, 
in which the substituents, independently of one another, have the following meanings:
R3 is hydrogen;
R4 is hydrogen;
Z1 and Z2 are hydrogen, C4-C10-alkyl, polymerizable groups or radicals carrying polymerizable groups,
where the definition of the variables Z1 and Z2 both in the general embodiment and in the preferred embodiment corresponds to the explanation already given above.
At least one of the radicals Z1 to Z3 is advantageously a polymerizable group or a radical containing a polymerizable group.
The abovementioned compounds are prepared in a manner known per se as described by U. Spohr et al., Can. J. Chem., 1993, 71(11), 1919-1927 and in DE-A-195 32 408, DE-A-44 08 171, EP-A-0 750 029 and in WO 95/16007. For further details, we refer to these specifications.
The invention also relates to chiral dopants of the general formula Ib 
in which the substituents, independently of one another, have the following meanings:
R1 is Z1xe2x80x94Y1xe2x80x94(A1)mxe2x80x94Y2xe2x80x94M1xe2x80x94Y3xe2x80x94(A2)nxe2x80x94Y4xe2x80x94;
R2 is hydrogen, C1-C12-alkyl, C1-C12-alkylcarbonyl, aryl, arylcarbonyl or Z2xe2x80x94Y5xe2x80x94(A3)oxe2x80x94Y6xe2x80x94M2xe2x80x94Y7xe2x80x94(A4)pxe2x80x94Y11xe2x80x94;
A1 to A4 are spacers having a chain length of from 1 to 30 carbon atoms;
M1 and M2 are mesogenic groups;
Y1 to Y7 are chemical bonds, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94, xe2x80x94C(xe2x95x90O)xe2x80x94N(R)xe2x80x94 or xe2x80x94(R) Nxe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94Oxe2x80x94CH2xe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94, xe2x80x94Nxe2x95x90CHxe2x80x94 or xe2x80x94Nxe2x95x90Nxe2x80x94;
Y11 is a chemicalbond, xe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94(R)Nxe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94CH2xe2x80x94 or xe2x80x94Oxe2x80x94CH2xe2x80x94;
R is hydrogen or C1-C4-alkyl;
Z1 and Z2 are hydrogen, C1-C12-alkyl, polymerizable groups or radicals carrying polymerizable groups;
m to p are 0 or 1,
where the radicals A1 to A4, Y1 to Y7 and Z1 and Z2 may be identical or different, and where, in the case where one or more of the indices m to p are zero, at least one of the radicals Y in each case adjacent to A is a chemical bond.
Preference is given to chiral dopants in which the substituents have the following meanings:
R1 is Z1xe2x80x94Y1xe2x80x94(A1)mxe2x80x94Y2xe2x80x94M1xe2x80x94Y3xe2x80x94(A2)nxe2x80x94Y4xe2x80x94;
R2 is Z2xe2x80x94Y5xe2x80x94(A3)oxe2x80x94Y6xe2x80x94M2xe2x80x94Y7xe2x80x94(A4)pxe2x80x94Y11xe2x80x94;
A1 and A3 are spacers having a chain length of from 1 to 6 carbon atoms;
Y1 to Y7 are chemical bonds, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94, xe2x80x94C(xe2x95x90O)xe2x80x94N(R)xe2x80x94 or xe2x80x94(R)Nxe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94CH2xe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94, xe2x80x94Nxe2x95x90CHxe2x80x94 or xe2x80x94Nxe2x95x90Nxe2x80x94;
Y11 is a chemical bond, xe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94(R)Nxe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94CH2xe2x80x94 or xe2x80x94Oxe2x80x94CH2xe2x80x94;
M1 and M2 are mesogenic radicals from the group consisting of: 
Z1 and Z2 are hydrogen, C4-C10-alkyl, polymerizable groups or radicals carrying polymerizable groups;
m is 0 or 1;
n is 0;
o is 0 or 1;
p is 0,
where at least one of the radicals Y3 and Y4 or Y7 and Y11 is a chemical bond.
Particular preference is given to chiral dopants of the general formula Ia, 
in which the substituents, independently of one another, have the following meanings:
Z1 and Z2 are hydrogen, C4-C10-alkyl, polymerizable groups or radicals carrying polymerizable groups.
The definition of the abovementioned variables in the general embodiment and in the preferred embodiment corresponds to the explanation already given above.
The invention also relates to cholesteric liquid-crystalline compositions comprising
a) at least one chiral liquid-crystalline monomer of the general formula I 
xe2x80x83or
b) a mixture of
b1) at least one achiral, liquid-crystalline, polymerizable monomer of the general formula II
Z4xe2x80x94Y13xe2x80x94(A7)sxe2x80x94Y14xe2x80x94M4xe2x80x94Y15xe2x80x94(A8)txe2x80x94Y16xe2x80x94Z5xe2x80x83xe2x80x83II
xe2x80x83in which the variables, independently of one another, have the following meanings:
A7 and A8 are spacers having a chain length of from 1 to 30 carbon atoms;
M4 is a mesogenic group;
Y13 to Y16 are chemical bonds, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94, xe2x80x94C(xe2x95x90O)xe2x80x94N(R7)xe2x80x94 or xe2x80x94(R7)Nxe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94CH2xe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94, xe2x80x94Nxe2x95x90CHxe2x80x94 or xe2x80x94Nxe2x95x90Nxe2x80x94;
R7 is hydrogen or C1-C4-alkyl;
s is 0 or 1;
t is 0 or 1;
Z4 and Z5 
are hydrogen, C1-C12-alkyl, polymerizable groups or radicals carrying polymerizable groups,
where the radicals A7 and A8 and Y13 to Y16 may be identical or different, at least one of the variables Z4 or Z5 is a polymerizable group or a radical carrying a polymerizable group, and, in the case where one or both of the indices s and t are zero, at least one of the radicals Y13 and Y14 or Y15 and Y16 is a chemical bond, and
b2) at least one chiral liquid-crystalline monomer of the general formula I.
In the case of the achiral liquid-crystalline monomers of the formula II, the same definitions and preferred embodiments apply for the polymerizable groups Z4 and Z5, the bridging members Y13 to Y16, the spacers A7 and A8 and the mesogenic group M4 as for the corresponding variables in the formula I.
Just as in formula I, it is also possible to link the mesogenic group directly to the radical Z4 or Z5. In these cases, s and/or t are 0 and Y13 and Y14 and/or Y15 and Y16 together are a chemical bond.
The mixture b) also contains at least one compound of the formula I already described above as chiral additive b2).
Suitable dopants should have a high twisting power in order that small amounts of the dopant are sufficient to induce the helical structure. In addition, the chiral dopants should exhibit good compatibility with the liquid-crystalline compounds so that an effective interaction between these components is enabled.
The extent of twist depends in each case on the twisting power of the chiral dopant and on its concentration. The pitch of the helix and in turn also the interference wavelength is thus dependent on the concentration of the chiral dopant. It is therefore not possible to indicate a generally applicable concentration range for the dopant. The dopant is added in the amount with which the desired UV reflection is achieved.
Preferred chiral additives for b2) are compounds of the formula I in which the substituents have the following meanings:
R1 is Z1xe2x80x94Y1xe2x80x94(A1)mxe2x80x94Y2xe2x80x94M1xe2x80x94Y3xe2x80x94(A2)nxe2x80x94Y4xe2x80x94;
R2 is Z2xe2x80x94Y5xe2x80x94(A3)oxe2x80x94Y6xe2x80x94M2xe2x80x94Y7xe2x80x94(A4)pxe2x80x94Y11xe2x80x94;
R3 and R4 are hydrogen;
A1 and A3 are spacers having a chain length of from 1 to 6 carbon atoms;
Y1 to Y7 are chemical bonds, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94;
Y11 is a chemical bond, xe2x80x94C(xe2x95x90O)xe2x80x94 or xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94;
M1 and M2 are mesogenic radicals from the group consisting of: 
Z1 and Z2 are hydrogen, C4-C10-alkyl, polymerizable groups or radicals carrying polymerizable groups;
m is 0 or 1;
n is 0;
o is 0 or 1; and
p is 0,
where at least one of the radicals Y3 and Y4 or Y7 and Y11 is a chemical bond.
Particularly preferred monomers II are the following structures: 
W1: CH2xe2x95x90CHxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94(CH2)4xe2x80x94Oxe2x80x94,
W2: xe2x80x94Oxe2x80x94(CH2)4xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94CHxe2x95x90CH2 
W3: CH2xe2x95x90CHxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94(CH2)6xe2x80x94Oxe2x80x94,
W4: xe2x80x94Oxe2x80x94(CH2)6xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94CHxe2x95x90CH2 
W5: CH2xe2x95x90C(CH3)xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94(CH2)4xe2x80x94Oxe2x80x94,
W6: xe2x80x94Oxe2x80x94(CH2)4xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94C(CH3)xe2x95x90CH2 
W7: CH2xe2x95x90C(CH3)xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94(CH2)6xe2x80x94Oxe2x80x94,
W8: xe2x80x94Oxe2x80x94(CH2)6xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94C(CH3)xe2x95x90CH2 
W9: CH2xe2x95x90CHxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94(CH2)4xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94,
W10: xe2x80x94Oxe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94(CH2)4xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94CHxe2x95x90CH2 
W11: CH2xe2x95x90CHxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94(CH2)6xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94,
W12: xe2x80x94Oxe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94(CH2)6xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94CHxe2x95x90CH2 
W13: CH2xe2x95x90C(CH3)xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94(CH2)4xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94,
W14: xe2x80x94Oxe2x80x94(Oxe2x95x90) Cxe2x80x94Oxe2x80x94(CH2)4xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94C(CH3)xe2x95x90CH2 
W15: CH2xe2x95x90C(CH3)xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94(CH2)6xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94,
W16: xe2x80x94Oxe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94(CH2)6xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94C(CH3)xe2x95x90CH2 
Particularly preferred monomers I are the following structures: 
W1: CH2xe2x95x90CHxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94(CH2)4xe2x80x94Oxe2x80x94
W2: xe2x80x94Oxe2x80x94(CH2)4xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94CHxe2x95x90CH2 
W3: CH2xe2x95x90CHxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94(CH2)6xe2x80x94Oxe2x80x94
W4: xe2x80x94Oxe2x80x94(CH2)6xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94CHxe2x95x90CH2 
W5: CH2xe2x95x90C(CH3)xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94(CH2)4xe2x80x94Oxe2x80x94,
W6: xe2x80x94Oxe2x80x94(CH2)4xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94C(CH3)xe2x95x90CH2 
W7: CH2xe2x95x90C(CH3)xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94(CH2)6xe2x80x94Oxe2x80x94,
W8: xe2x80x94Oxe2x80x94(CH2)6xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94C(CH3)xe2x95x90CH2 
W9: CH2xe2x95x90CHxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94(CH2)4xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94
W10: xe2x80x94Oxe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94(CH2)4xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94CHxe2x95x90CH2 
W11: CH2xe2x95x90CHxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94(CH2)6xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94
W12: xe2x80x94Oxe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94(CH2)6xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94CHxe2x95x90CH2 
W13: CH2xe2x95x90C(CH3)xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94(CH2)4xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94,
W14: xe2x80x94Oxe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94(CH2)4xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94C(CH3)xe2x95x90CH2 
W15: CH2xe2x95x90C(CH3)xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94(CH2)6xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94,
W16: xe2x80x94Oxe2x80x94(Oxe2x95x90)Cxe2x80x94Oxe2x80x94(CH2)6xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94C(CH3)xe2x95x90CH2 
The weight ratios between components II and I are in the range from 99:1 to 40:60, preferably in the range from 99:1 to 70:30, particularly preferably from 98:2 to 85:15.
A particular characteristic of the above cholesteric liquid-crystalline compositions is that they reflect left-handed circular-polarized light.
Use of the cholesteric liquid-crystalline compositions according to the invention in cosmetic and pharmaceutical preparations:
The light protection agents used in cosmetic and pharmaceutical preparations have the job of eliminating or at least reducing harmful effects of sunlight on the human skin. In addition, however, these light protection agents also serve to protect other ingredients against destruction or degradation by UV radiation. In hair-cosmetic formulations, the aim is to reduce damage to keratin fibers by UV rays.
The sunlight reaching the earth""surface has a UV-B component (280 to 320 nm) and a UV-A component ( greater than 320 nm) directly adjacent to the visible region of light. The effect on the human skin is particularly evident in the case of UV-B radiation in the form of sunburn. Accordingly, the industry offers a relatively large number of substances which absorb UV-B radiation and thus prevent sunburn.
Dermatological investigations have shown that UV-A radiation is also entirely capable of causing skin damage and allergies, for example by damaging the keratin or elastin. This results in a reduction in elasticity and water storage capacity of the skin, i.e. the skin becomes less flexible and tends to wrinkle. The strikingly high frequency of skin cancer in regions of strong sunlight shows that damage to genetic information in the cells is apparently also caused by sunlight, especially by UV-A radiation. All this knowledge therefore makes the development of efficient filter substances for the UV-A and UV-B regions appear necessary.
In addition to known UV absorbers, for example 2-ethylhexyl 4-methoxycinnamate and 3-(4xe2x80x2-methyl)benzylidenebornan-2-one, light protection agents which, in the form of pigments, reflect or absorb UV rays are frequently also used in cosmetic and pharmaceutical formulations. The most important of these pigments are titanium dioxide and zinc oxide. At high concentrations, pigments can achieve full screening of the skin. However, the particles then reflect not only UV radiation, but also visible light, causing the frequently undesired strong inherent coloration of pigment-containing preparations.
Whereas titanium dioxide pigments with coarse particles (particle size greater than 500 nm) have a comparable action in the UV-B and UV-A regions, the spectrum of action shifts toward the UV-B with decreasing particle size in the case of finely divided material. This shows that the absorption/reflection characteristics are directly dependent on the size and distribution of the particles. Balanced UV-B and UV-A protection therefore requires certain particle-size distributions.
It has been found to be disadvantageous on use of the abovementioned pigments that agglomeration, aggregation and/or separation of the pigment particles frequently occurs during storage of the cosmetic or pharmaceutical light protection agent formulations. The consequence of the modified optical properties can be a drastically reduced light protection action.
As an alternative to the abovementioned pigments, DE-A-196 19 460 describes the use of liquid-crystal mixtures having a cholesteric phase comprising a) liquid-crystalline organosiloxanes containing dianhydrohexitol derivatives as chiral groups, and b) chiral monomeric additives which induce the same helicity as the respective liquid-crystalline organosiloxanes, for the production of UV protection layers, in the form of films or flakes, which are suitable for cosmetic purposes. The liquid-crystal mixtures described here have the disadvantage that they can be converted into pigments only unsatisfactorily owing to their high viscosity.
DE-A-196 29 761 describes cosmetic or pharmaceutical preparations comprising polyorganosiloxane pigments having a viewing angle-dependent color. The pigments are at least one oriented, crosslinked substance of a liquid-crystalline structure with a chiral phase. Although the pigments disclosed here in the cosmetic and pharmaceutical formulations have certain absorption properties in the UV region, they have the disadvantage for certain applications of being colored compounds, whose range of applications is consequently restricted. However, there is very frequently a demand for precisely those cosmetic and pharmaceutical preparations by means of which UV protection is achieved, but in which coloration of the preparation is undesired.
The present invention therefore also relates to the use of the abovementioned cholesteric liquid-crystalline compositions as UV filters in cosmetic and pharmaceutical preparations for protecting the human skin or human hair against sunlight, alone or together with UV-absorbent compounds which are known per se for cosmetic and pharmaceutical preparations.
The cholesteric liquid-crystalline compositions used which are preferred for use as UV filters in cosmetic and pharmaceutical preparations comprise a mixture of at least one achiral; liquid-crystalline, polymerizable monomer of the formula II and at least one chiral polymerizable monomer of the formula I.
For the novel use of the abovementioned cholesteric liquid-crystalline compositions a) and b) as UV filters in cosmetic and pharmaceutical preparations, the components of the formulae I and II present in these compositions can be incorporated directly into the cosmetic and pharmaceutical preparations.
Preferably, however, the cholesteric liquid-crystalline compositions used in accordance with the invention are employed in the form of pigments. These pigments are obtainable by converting the monomers I and II present in the cholesteric liquid-crystalline compositions into highly crosslinked polymers having a frozen liquid-crystalline order structure with the aid of their polymerizable groups by free-radical or ionic polymerization processes, which can be initiated by a photochemical reaction.
The preparation of these pigments is known and is described in detail in, inter alia, German Application P 19738369.6.
In addition, an overview of processes for the photochemical crosslinking of oriented starting materials is given in C. G. Roffey, Photopolymerisation of Surface Coatings, (1982) John Willey and Sons, Chichester, pp. 137 to 208.
In a preferred embodiment, the three-dimensionally crosslinkable, polymerizable monomers are applied to a substrate, crosslinked on this substrate and detached from the substrate after the crosslinking.
The cholesteric liquid-crystalline compositions which have been crosslinked to give a film can, after the polymerization, be comminuted to the particle size desired in each case by grinding. Depending on the desired application and the type of cosmetic or pharmaceutical formulation, particles having a diameter of from 1 to 1000 xcexcm can be produced. Preferred particle sizes are in the range from 1 to 100 xcexcm, particularly preferably in the range from 15 to 50 xcexcm.
The thickness of the pigments is from 1 to 100 xcexcm, preferably from 1 to 50 xcexcm, particularly preferably from 1.5 to 10 xcexcm.
The cholesteric liquid-crystalline compositions a) and b) which are suitable as starting substances for the preparation of the pigments have a twisted structure with a pitch corresponding to a light wavelength of up to 450 nm. As shown in the preferred embodiments b), these twisted structures having a defined pitch can be obtained from nematic structures b1) by adding a chiral substance b2). The nature and proportion of the chiral substance determine the pitch of the twisted structure and thus the wavelength of the reflected light. Depending on the chirality of the optically active additives employed, the twist of the structure can be either left-handed or right-handed.
So-called broad-band reflectors can be produced by simply mixing a plurality of the cholesteric liquid-crystalline pigments to be used in accordance with the invention, each with different UV reflection maxima.
In addition, it is possible to achieve complete reflection of the UV rays by mixing at least two different pigments in the cholesteric liquid-crystalline compositions a) and/or b) with opposite twist (helicity). Pigments having such cholesteric liquid-crystalline structures of opposite twist are obtainable, for example, by adding the individual mirror-image isomers (enantiomers) or diastereomers of the chiral additives b2) to the achiral, liquid-crystalline, polymerizable monomer b1). The pitch of the structures of opposite twist can be identical or different.
It is also possible firstly to mix the cholesteric liquid-crystalline compositions a) or b) of opposite twist and then to convert the mixture into the above-described pigments by the abovementioned crosslinking and to employ the pigments as UV reflectors in cosmetic and pharmaceutical formulations.
Besides the abovementioned mixtures of cholesteric liquid-crystalline pigments, it is also possible to prepare multilayer pigments whose individual layers comprise different three-dimensionally crosslinked cholesteric liquid-crystalline compositions to be used in accordance with the invention. The design of such multilayer pigments can be varied widely. Thus, inter alia,
individual layers of crosslinked cholesteric liquid-crystalline compositions of opposite twist or
individual layers of crosslinked cholesteric liquid-crystalline compositions having the same twist direction, but different pitch and thus different reflection properties,
can be applied one on top of the other.
Preference is given to so-called three-layer pigments, in which the two outer layers each consist of at least one of the crosslinked, cholesteric liquid-crystalline compositions to be used in accordance with the invention, and the middle layer can comprise, for example, a binder matrix, in which, in addition, a further UV absorber may be incorporated. Details on the preparation, properties and further constituents of such multilayered, cholesteric pigments are given in German Patent Application P 19738368.8.
The invention thus also relates to the above-described pigments, in particular multilayer pigments, comprising the cholesteric liquid-crystalline compositions mentioned at the outset.
An advantage of the pigments used in accordance with the invention is that their composition can be customized so that the desired UV reflection can be achieved using these pigments without exhibiting any inherent color (in the visible region).
A further advantage of the pigments consists in their physical properties. Owing to their low density (compared, for example, with TiO2), the pigments can readily be incorporated into emulsions without any aggregation or separation of pigment particles.
The pigments to be used in accordance with the invention can be incorporated into the cosmetic and pharmaceutical preparations by simple mixing.
The present invention furthermore relates to cosmetic and pharmaceutical preparations comprising from 0.1 to 20% by weight, preferably from 0.5 to 10% by weight, particularly preferably from 1 to 7% by weight, based on the total amount of the cosmetic and pharmaceutical preparation, of one or more of the cholesteric liquid-crystalline compositions comprising a) at least one chiral, liquid-crystalline, polymerizable monomer of the general formula I, by means of which a cholesteric liquid-crystalline phase with a pitch of less than 450 nm can be achieved, or b) a mixture of at least one achiral, liquid-crystalline, polymerizable monomer of the general formula II and at least one chiral, liquid-crystalline, polymerizable monomer of the general formula I, by means of which a cholesteric liquid-crystalline phase with a pitch of less than 450 nm can be achieved, together with compounds which absorb in the UV-A and UV-B region which are known per se for cosmetic and pharmaceutical preparations, as light protection agents. The variables in the formulae I and II and the class of the chiral additives employed correspond, in both their general and preferred embodiments, to the explanations already outlined above.
Preference is given to those of the abovementioned cosmetic and pharmaceutical preparations which comprise the cholesteric liquid-crystalline compositions to be used in accordance with the invention in the form of the pigments described above, in particular in the form of multilayered pigments.
The cosmetic and pharmaceutical preparations containing light protection agents are generally based on a carrier comprising at least one oil phase. However, preparations based exclusively on water are also possible if compounds having hydrophilic substituents are used. Accordingly, oils, oil-in-water and water-in-oil emulsions, creams and pastes, compositions for lip protection sticks and fat-free gels are suitable.
Sun protection preparations of this type can accordingly be in liquid, pasty or solid form, for example as water-in-oil creams, oil-in-water creams and lotions, aerosol foam creams, gels, oils, fat sticks, powders, sprays or alcoholic/aqueous lotions.
Conventional oil components in cosmetics are, for example, paraffin oil, glyceryl stearate, isopropyl myristate, diisopropyl adipate, stearyl 2-ethylhexanoate, hydrogenated polyisobutene, vaseline, caprylic acid/caproic acid triglycerides, microcrystalline wax, lanolin and stearic acid.
Conventional cosmetic auxiliaries which are suitable as additives are, for example, coemulsifiers, fats and waxes, stabilizers, thickeners, biogenic active ingredients, film formers, fragrances, colorants, pearlescent agents, preservatives, pigments, electrolytes (for example magnesium sulfate) and pH regulators. Preferred coemulsifiers are known W/O and also O/W emulsifiers, for example polyglycerol esters, sorbitan esters and partially esterified glycerides. Typical examples of fats are glycerides; waxes include beeswax, paraffin wax and microwaxes, if desired in combination with hydrophilic waxes. Suitable stabilizers are metal salts of fatty acids, for example magnesium stearate, aluminum stearate and/or zinc stearate. Examples of suitable thickeners are crosslinked polyacrylic acids and derivatives thereof, polysaccharides, in particular xanthan gum, guar guar, agar agar, alginates and tyloses, carboxymethylcellulose and hydroxyethylcellulose, furthermore fatty alcohols, monoglycerides and fatty acids, polyacrylates, polyvinyl alcohol and polyvinylpyrrolidone. The term biogenic active ingredients is taken to mean, for example, plant extracts, albumen hydrolyzates and vitamin complexes. Customary film formers are, for example, hydrocolloids, such as chitosan, microcrystalline chitosan and quaternized chitosan, polyvinylpyrrolidone, vinylpyrrolidone-vinyl acetate copolymers, acrylic acid polymers, quaternary cellulose derivatives and similar compounds. Examples of suitable preservatives are formaldehyde solution, p-hydroxybenzoate and sorbic acid. Examples of suitable pearlescent agents are glycol distearic esters, such as ethylene glycol distearate, but also fatty acids and fatty acid monoglycol esters. Suitable colorants are the substances which are suitable and approved for cosmetic purposes, as listed, for example, in the publication xe2x80x9cKosmetische Fxc3xa4drbemittelxe2x80x9d [Cosmetic Colorants] by the Farbstoffkommission der Deutschen Forschungsgemeinschaft, published by Verlag Chemie, Weinheim, 1984. These colorants are usually employed in concentrations of from 0.001 to 0.1% by weight, based on the total mixture.
The preparations according to the invention advantageously comprise one or more antioxidants. Favorable, but nevertheless optional antioxidants are all natural, synthetic and/or partially synthetic antioxidants which are suitable or customary for cosmetic and/or dermatological applications.
The antioxidants are particularly advantageously selected from the group consisting of:
amino acids (for example glycine, histidine, tyrosine and tryptophan) and derivatives thereof, imidazoles (for example urocaninic acid) and derivatives thereof, peptides, such as D,L-carnosine, D-carnosine, L-carnosine and derivatives thereof (for example anserine), carotenoids (for example xcex2-carotene and lycopine) and derivatives thereof, lipoic acid and derivatives thereof (for example dihydrolipoic acid), aurothioglucose, propylthiouracil and other thio compounds (for example thioredoxin, glutathione, cysteine, cystine, cystamine and the glycosyl, N-acetyl, methyl, ethyl, propyl, amyl, butyl, lauryl, palmitoyl, oleyl, xcex3-linoyl, cholesteryl and glyceryl esters thereof) and salts thereof, dilauryl thiodipropionate, distearyl thiodipropionate, thiodipropionic acid and derivatives thereof (esters, ethers, peptides, lipids, nucleotides, nucleosides and salts) and sulfoximine compounds (for example buthionine sulfoximine, homocysteine sulfoximine, buthionine sulfone, penta-, hexa- and heptathionine sulfoximine) in very small compatible dosages (for example pmol to xcexcmol/kg), furthermore (metal) chelators (for example xcex1-hydroxy fatty acids, palmitic acid, phytic acid and lactoferrin), xcex1-hydroxy acids (for example citric acid, lactic acid and malic acid), humic acid, bile acid, bile extracts, biliburin, biliverdin, EDTA, EGTA and derivatives thereof, unsaturated fatty acids and derivatives thereof (for example xcex3-linolenic acid, linoleic acid and oleic acid), folic acid and derivatives thereof, (for example 5-methyltetrahydrofolic acid), ubiquinone and ubiquinol and derivatives thereof, vitamin C and derivatives thereof (for example ascorbyl palmitate, ascorbyl phosphates and ascorbyl acetates), tocopherols and derivatives thereof (for example tocopheryl acetate and tocotrienol), vitamin A and derivatives (for example vitamin A palmitate), rutinic acid and derivatives thereof, ferulic acid and derivatives thereof, butylhydroxytoluene, butylhydroxyanisol, nordihydroguaiacic acid, nordihydroguaiaretic acid, trihydroxybutyrophenone, uric acid and derivatives thereof, stilbenes and derivatives thereof.
The total proportion of the auxiliaries and additives can be from 1 to 80% by weight, preferably from 6 to 40% by weight, and the non-aqueous component (xe2x80x9cactive substancexe2x80x9d) can be from 20 to 80% by weight, preferably from 30 to 70% by weight, based on the preparation. The preparation can be prepared in a manner known per se, for example by hot, cold, hot/cold or PIT emulsification. These are purely mechanical processes, with no chemical reaction.
Finally, further UV-absorbent substances known per se can also be used as long as they are stable in the overall system of the combination of UV filters to be used in accordance with the invention.
The majority of the light protection agents in the cosmetic and pharmaceutical preparations serving to protect the human epidermis consist of compounds which absorb UV light in the UV-B region, i.e. in the region from 280 to 320 nm. For example, the proportion of cholesteric liquid-crystalline compositions to be used in accordance with the invention is from 10 to 90% by weight, preferably from 20 to 70% by weight, based on the total amount of UV-B- and UV-A-absorbent substances.
Suitable UV filter substances which can be used in combination with the cholesteric liquid-crystalline compositions to be used in accordance with the invention are any desired UV-A and UV-B filter substances. The following may be mentioned by way of example:
Finally, mention should also be made of micronized pigments, such as titanium dioxide and zinc oxide.
For protection of human hair against UV rays, the cholesteric liquid-crystalline compositions a) and/or b) used in accordance with the invention can be incorporated into shampoos, lotions, gels, hair sprays, aerosol foam creams or emulsions in concentrations of from 0.1 to 20% by weight, preferably from 0.5 to 10% by weight, particularly preferably from 1 to 7% by weight. The respective formulations can be used, inter alia, for washing, coloring and styling hair.
The compositions to be used in accordance with the invention are generally distinguished by a particularly high reflection capacity in the region of UV-A and UV-B radiation with a sharp band structure. They can furthermore readily be incorporated into cosmetic and pharmaceutical formulations. In addition, they are particularly distinguished by their high photostability, and the preparations prepared therewith by their pleasant feel on the skin.
The UV filter action of the cholesteric liquid-crystalline compositions a) and/or b) used in accordance with the invention can also be utilized for stabilization of active ingredients and auxiliaries in cosmetic and pharmaceutical formulations.